This invention generally relates to cryogenic storage apparatus and, more specifically, to a unique and advantageous venting system employed in the lid or closure member of the apparatus.
Many types of cryogenic storage units exist for various scientific or industrial purposes. These units rely on methods of refrigeration that allow items to be cooled often below 100.degree. C. For some of coldest storage applications, liquid cryogen, such as nitrogen, is contained within a tank and the items to be stored or otherwise treated are simply immersed in this bath of liquid cryogen.
As liquid cryogens generally evaporate at ambient temperatures and pressures, there should be a venting system employed in these units. Otherwise, the units must be manufactured as pressure vessels and, in such situations, access to any items stored within the units would be limited and difficult. Typically, the venting systems employed in top opening units used, for example, to store scientific samples and other accessible items have involved peripheral venting about the upper lid of the unit. This peripheral venting involves using discontinuous seals about the periphery of the lid. That is, vents are provided generally between the lid and the housing of the unit at spaced peripheral regions around the unit.
Unfortunately, the peripheral venting around the unit has led to various disadvantages and ill effects. For example, frost and ice build up on the outside of the unit adjacent to the vents when the cold gas meets humid ambient air. These vents may also lead to the escape of more liquid cryogen from the storage tank than is necessary to allow for gas expansion within the tank. Thus, depletion of the liquid cryogen through evaporation may occur more rapidly than necessary.
With this background in mind, it would be desirable to provide a cryogenic, liquid cryogen storage apparatus having a venting system which better inhibits the formation of frost or ice around the periphery of the lid and housing and which also more readily regulates the escape cryogen gas.